1. Field of the Invention
This invention relates to a gun for effecting the perforation of the casing and adjacent formation of a well, and particularly to a perforating gun wherein the firing of the gun is accomplished through the utilization of fluid pressure forces.
2. Description of the Prior Art
Perforating guns have long been employed to effect the perforation of a well casing in the vicinity of a production zone and to produce fractures extending into such production zone. The popular perforating guns now uniformly employ the so-called "shaped charges", which are disposed in vertically and angularly spaced relationship relative to the casing axis so as to produce a large number of evenly spaced perforations with a single firing. Such shaped charges are generally ignited by a primacord which contacts a primer end of each shaped charge container to ignite a primer contained within each such container.
The ignition of the primacord is commonly accomplished by either electronically actuating a detonator or by dropping a weight or bar on an impact actuated primer or detonator which is stationarily positioned immediately above the perforating gun housing and is connected to the primacord which extends downwardly through the perforating gun housing. The employment of a detonating bar dropped through a tubular conduit as a means for effecting the ignition and discharge of the perforating gun has encountered difficulties in those wells wherein the well bore deviates substantially from the true vertical when passing through a particular production zone. The deviation may be sufficiently great so that the fall speed of the detonating bar is substantially reduced to the point that insufficient impact energy is imparted to the primer to effect its discharge. In other wells where it is neccessary to employ a high density kill fluid or the like, the existence of such fluid in the conduit bore through which the detonating bar is dropped can very well reduce the speed of the detonating bar to an ineffective level. Such failures to detonate the primer obviously imposes a substantial cost and time penalty on the completion of the well, since the detonating bar must be engaged by a fishing tool, pulled back up to a high level in the well and again dropped to hopefully effect the ignition of the primer on the next try. The hydraulic firing head will also be useful in heavy mud situations where particulates deposit on a mechanical firing head which can reduce bar impact.